Hi. I got very interested Poco library.I needed to write a smtp email client that would be supported socks protocol. But i haven't found implementation of this protocol in Poco. If you are interested in my implementation of the sock protocol, I can send you this code.

Yes, I implement SocksProxyImpl a subclass of StreamSocketImpl.
I realize support a socks proxy chain but it is not compleate.
My realization does not support the installation of different passwords for socks proxy servers. I'll read in detail your coding standards and send my code to you.
In addition to the protocol Socks, I realized the expansion of HTTP to work through the method CONNECT. But all this is not enough tested.